The invention relates to method and apparatus for making diapers with elastic bands in the leg contracting zone of the diaper. U.S. Pat. No. 4,081,301 and my U.S. Pat. No. 4,227,952 are illustrative of patents which show diaper making apparatus with elastic band applying stations.
In prior art techniques the elastic band is stretched prior to application to the backing or facing sheet. Methods that use or apply elastic bands in a stretched condition are not suitable for applying an extruded elastomeric band in a heat softened state directly to the backing or facing.
With prior art techniques the elastic strips or ribbons have a uniform cross-section throughout their length. Hence, when relaxed and upon application of the diaper to the baby, have the same tension throughout the crotch length. As a result, some portions of the elastic member cause a high degree of stress concentration that may result in pinching, indenting, marking and irritation of the baby's skin.
The methods of applying pre-formed elastic band material from bulk containers of elastic band also have associated problems involving splicing, threading, alignment and application to webs. In addition, uniformity in tension during assembly is also a problem. The difficulties in manipulating pre-formed elastic ribbons also limit the shapes and patterns of elastic members as well as their placement on the diaper. Normally it is difficult to place an elastic member under tension on a web in other than a straight line path because of the tendency of the stretched elastic member to return to a straight line.
U.S. Pat. No. 4,379,016 discloses the application of or formation in situ of an elastic ribbon by spraying across folds and filling the folds with the sprayed material. This arrangement requires self bonding or adherence of the elastic material to the web and may limit the web materials which can be utilized and which will bond with the sprayed ribbon.
In addition to the difficulties in handling and applying pre-formed elastic ribbons the cost of elastic ribbon material is exceedingly high. My prior U.S. Pat. No. 4,227,952 has succeeded in reducing the cost of the length of elastic band employed to about 50% of an elastic ribbon, the full length of a diaper.